>Not knowing that words sometimes take on different meanings when they become part of another language.
>Not knowing that "otaku" has at least 3 meanings even in Japan. (Fun fact: otakus in Japan wear the title like a badge of honor.)
Fantastic!

I suppose. otaku's most direct meaning is "fanatic"
You can be a fanatic of many things but some weaboos decided to start calling themselves otakus thinking it meant hardcore anime fan and thus otaku and weaboo now mean the same thing to society.